Pneumatic tires

Abstract: A pneumatic tire for small passenger vehicles having a pair of bead portions located at the internal periphery of a pair of sidewalls connected to a tread at both its edges, characterized in that the bead core (1) of the bead portion is a mono strand bead core, and the section of the bead core is a close-packed structure unit made of 3 to 20 wires (2); the diameter (D) of the wires is 1.2 to 1.8 mm, and the ratio (H/D) of the distance (H) between the centers of adjacent wires to the diameter (D) of the wires is 1.01 to 1.20; and the sectional configuration of the bead core is such that N(2) = N(1) + 1 , where N(1) is the wire number of the first row and N(2) is the wire number of the second row counted from the bead base side. It is possible to improve steering characteristics (manoeuvrability) of such a pneumatic tire for small passenger vehicles by restraining the disorder of uniformity of the tire in the circumferential and longitudinal directions.

Description: The present invention relates to pneumatic tires, and in particular to pneumatic tires for small passenger vehicles having good steering characteristics by improving the bead construction of the tire. The bead core of the bead portion of a pneumatic tire has a function of locating and fixing textile or steel cords of a carcass ply and a function of determining the internal periphery of the tire body and engaging the tire with a wheel rim. Thus, the bead core is a very important component part in a pneumatic tire, and various kinds of constructions of bead core have been proposed. For example, as shown in Figure 5 of the accompanying drawings, it is well known to construct a bead core 10 by winding a strip 11 of wire-rubber matrix made of one row of several wires 12 buried in rubber 13. The sectional configuration of such a bead core is shown in Figure 6. However, in manufacturing a pneumatic tire having the above-mentioned bead core obtained by winding a strip of wire-rubber matrix or other conventional bead core, the rows and lines of the wire-rubber matrix tend to fall into disorder during tire building and curing, and it is very difficult to maintain uniformity of tires in circumferential and longitudinal directions. Consequently, the steering characteristics (manoeuvrability) of the tires thus manufactured are adversely affected. A prior art tire disclosing the features of the preamble of claim 1 is shown e.g. by US-A-5 010 938. It is an object of the present invention to provide a pneumatic tire for small passenger vehicles having improved steering characteristics (manoeuvrability) by restraining the disorder of uniformity of tires in the circumferential and longitudinal directions. The present invention provides a pneumatic tire, particularly for small passenger vehicles, having a pair of bead portions located at the internal periphery of a pair of sidewalls connected to a tread at both edges thereof, the bead core of the bead portion being a mono strand bead core made of rubberized circular-section wires spirally wound and bundled, characterized in that: (a) the section of the bead core is a close-packed structure unit made of 3 to 20 wires; (b) the diameter (D) of the wires is 1.2 to 2.2 mm, and the ratio (H/D) of the distance (H) between the centers of adjacent wires to the diameter (D) of the wires is 1.01 to 1.20; and (c) the sectional configuration of the bead core is such that N(2) = N(1) + 1 , where N(1) is the wire number of the first row and N(2) is the wire number of the second row counted from the bead base side. It is preferable that the section of the bead core has a regular hexagon of close-packed structure made of 7 wires. The storage modulus (E') at 30°C of the rubber between the wires is preferably not less than 3.0 x 10 8 dyn/cm 2 , and more preferably not less than 1.0 x 10 9 dyn/cm 2 . In accordance with the present invention, the bead core is a mono strand bead core and comprises a close-packed structure unit, the section of which is made of 3 to 20 wires. If the number of wires is less than 3, the close-packed structure unit is not obtained. If the number of wires is greater than 20, the weight of the tire is increased and it becomes difficult to assemble the tire on a rim. Also, in accordance with the present invention, the diameter (D) of the wires is 1.2 to 2.2 mm, and the ratio (H/D) of the distance (H) between the centers of adjacent wires to the diameter (D) of the wires is 1.01 to 1.20. If the diameter (D) of the wires is less than 1.2 mm, the rigidity and strength of the bead core are not sufficient; while if the diameter (D) of the wires is more than 2.2 mm, the weight of the tire is increased and it becomes difficult to assemble the tire on a rim. If the above ratio (H/D) is less than 1.01, since the structural rigidity of the bead core ring becomes too high, it becomes difficult to assemble the tire on a rim; while if the ratio (H/D) is more than 1.20, since deformation of the bead core during tire building and curing becomes large, tire uniformity is deteriorated. It is preferable that the diameter (D) of the wires is 1.2 to 1.8 mm and the above ratio (H/D) is in the range of 1.05 and 1.15. Further, in accordance with the present invention, the configuration of the bead core in the section including the tire rotating axis is such that N(2) = N(1) + 1 , where N(1) is the wire number (number of wires) of the first row and N(2) is the wire number of the second row. This configuration is necessary for reducing moment given to the bead core by the carcass ply during tire building and curing. This configuration makes the deformation of the bead core small and restrains the disorder of uniformity of tires in the circumferential and longitudinal directions, and therefore improves stable steering characteristics (manoeuvrability). In the following description, reference will be made to the accompanying drawings, in which: Figure 1 is a cross-section view showing a bead core configuration in the section including the tire rotating axis; Figure 2 is a cross-section view showing another bead core configuration in the section including the tire rotating axis; Figure 3 is a cross-section view showing yet another bead core configuration in the section including the tire rotating axis; Figure 4 is an enlarged cross section view of a bead core in accordance with the invention; Figure 5 is a perspective view of a bead core of the prior art; and Figure 6 is a cross-section view of the prior art bead core configuration shown in Figure 5 in the section including the tire rotating axis. If the section of the bead core has a regular hexagon of close-packed structure made of 7 wires, the above-mentioned moment given to the bead core by the carcass ply during tire building and curing is much more reduced and the deformation of the bead core during tire building and curing becomes small. Here, "the section of the bead core having regular hexagon of close-packed structure made of 7 wires" means both (1) the section of the bead core 1 shown in Figure 1 and Figure 2, where an arbitrary set or group of 7 wires 2 constitutes a regular hexagon of close-packed structure, and (2) the section of the bead core 1 shown in Figure 3, where all the wires 2 constitute a regular hexagon of close-packed structure. In Figures 1, 2 and 3, the wires 2 are buried in rubber 3. To reduce rubber flow and to make the deformation of the bead core during tire building and curing small, it is preferable that the storage modulus (E') at 30°C of the rubber 3 between the wires 2 is not less than 3.0 x 10 8 dyn/cm 2 , more preferably not less than 1.0 x 10 9 dyn/cm 2 . In accordance with the invention, since the bead core is constructed as mentioned above, it is possible to use bead wires having a larger diameter than conventional ones. Thus, the number of windings of a mono strand bead is reduced and bead breaking pressure becomes higher. Consequently, in accordance with the invention, reduction of tire weight and reduction of tire material and manufacturing cost are achieved. The invention will be further described with reference to the following examples. In the examples, the configurations of the bead core in the section including the tire rotating axis are as shown in Figure 6 (construction 1.), as shown in Figure 1 (construction 2.), as shown in Figure 2 (construction 3.), and as shown in Figure 3 (construction 4.). Bead cores having various values of wire diameter (D) and ratio (H/D) of the distance (H) between the centers of adjacent wires to the diameter (D) of the wires (see Figure 4), and storage modulus (E') at 30°C of the rubber between the wires as shown in Tables 1 to 3 below were tested in view of time required for rim mounting (hereinafter defined). Also, steering characteristics (manoeuvrability) of tires having the above bead cores were evaluated. The tire size was 205/65 R15. Storage modulus (E'), time required for rim mounting, and steering characteristics (manoeuvrability) are evaluated as follows. Storage modulus (E') Test samples of 5 mm width and 20 mm length are cut out from slab sheet rubber of 2 mm thickness cured under the condition of 160°C x 15 minutes. Storage modulus (E') of each sample is measured by a spectrometer made by Iwamoto Seisakusho K.K. under the condition that initial load is 160g, dynamic strain is 1%, frequency is 52 Hz, and temperature is 30°C. Time for rim mounting The average time (t) required for rim mounting is measured after 10 tires of each tire size 155/65 R12, 175/70 R13 and 205/65 R15 are mounted on a rim of 12 x 4.00B, 5J-13 and 6J-15 respectively. The average time (t) required for rim mounting of a comparison tire of construction 1. is defined to be t 0 and used as a control. Index of (t 0 /t) x 100 is shown in the Tables for each tire. The higher the index, the better the results. An index of more than 80 is satisfactory. Steering characteristics (manoeuvrability) Steering characteristics (manoeuvrability) are evaluated by feeling by a test driver after driving passenger vehicles on which test tires are mounted. Test results are shown by an index, where index 100 represents the result of the comparison tire. The results of the evaluation are shown in Tables 1 to 3 below. C-1 E-1 C-2 C-3 E-2 E-3 E-4 construction No. shown in Figures 1. 2. 2. 2. 2. 2. 2. wire diameter 0.96 1.40 1.40 1.40 1.40 1.40 1.40 H/D 1.30 1.14 1.008 1.23 1.03 1.18 1.14 storage modulus (E')(x 10 8 dyn/cm 2 ) 1.8 3.3 3.3 3.3 3.3 3.3 1.8 rim mounting 100 98 52 118 87 107 105 manoeuvrability 100 120 106 98 115 107 101 E-5 E-6 C-4 E-7 E-8 C-5 E-9 construction No. shown in Figures 2. 2. 1. 3. 3. 4. 4. wire diameter 1.40 1.40 0.96 1.20 1.20 1.80 1.80 H/D 1.14 1.14 1.30 1.17 1.12 1.008 1.03 storage modulus (E')(x 10 8 dyn/cm 2 ) 5.0 12 5.0 5.0 5.0 3.3 3.3 rim mounting 98 97 99 100 99 50 91 manoeuvrability 123 126 99 114 120 107 110 E-10 E-11 C-6 E-12 E-13 E-14 E-15 construction No. shown in Figures 4. 4. 4. 4. 4. 4. 4. wire diameter 1.80 1.80 1.80 1.80 1.80 1.80 1.80 H/D 1.10 1.16 1.23 1.16 1.16 1.16 1.16 storage modulus (E')(x 10 8 dyn/cm 2 ) 3.3 3.3 3.3 1.8 5.0 12 50 rim mounting 96 99 104 103 98 97 95 manoeuvrability 115 123 102 100 124 128 131 In the above Tables 1 to 3, C-1 to C-6 are comparison tires, and E-1 to E-15 are tires in accordance with the present invention. As described in the above, since tires for small passenger vehicles in accordance with the invention have a pair of mono strand bead cores of special construction, steering characteristics (manoeuvrability) are improved without bringing about difficulties in assembling the tire on a rim. Also, in accordance with the invention, since the bead wires have larger diameter than conventional ones, the number of windings of a mono strand bead is reduced and bead breaking pressure becomes higher, and consequently it is possible to reduce tire weight and tire manufacturing cost.

Claims: A pneumatic tire, particularly for small passenger vehicles, having a pair of bead portions located at the internal periphery of a pair of sidewalls connected to a tread at both edges thereof, the bead core (1) of the bead portion being a mono strand bead core made of rubberized circular-section wires (2) spirally wound and bundled, characterized in that: (a) the section of the bead core is a close-packed structure unit made of 3 to 20 wires; (b) the diameter (D) of the wires is 1.2 to 2.2 mm, and the ratio (H/D) of the distance (H) between the centers of adjacent wires to the diameter (D) of the wires is 1.01 to 1.20; and (c) the sectional configuration of the bead core is such that N(2) = N(1) + 1 , where N(1) is the wire number of the first row and N(2) is the wire number of the second row counted from the bead base side. A pneumatic tire as claimed in claim 1, characterized in that the section of the bead core (1) has a regular hexagon of close-packed structure made of 7 wires (2). A pneumatic tire as claimed in claim 1 or 2, characterized in that the storage modulus (E') at 30°C of the rubber (3) between the wires (2) is not less than 3.0 x 10 8 dyn/cm 2 . A pneumatic tire as claimed in claim 3, characterized in that said storage modulus (E') is not less than 1.0 x 10 9 dyn/cm 2 . A pneumatic tire as claimed in any of claims 1 to 4, characterized in that said diameter (D) of the wires is 1.2 to 1.8 mm, and said ratio (H/D) is 1.05 to 1.15.

Inventors: YAMAMOTO MASAHIKO, YAMAMOTO, MASAHIKO
Applicants: BRIDGESTONE CORP, BRIDGESTONE CORPORATION
Application year: 1994
Main classification: B60C15
IPC codes: B29D30, B60C15, B60C9